1. Field of the Disclosure
The present invention relates in general to stimulating oil and gas wells and, in particular, to a system, method and apparatus for a fracturing process for wells having a liner, such as a cemented-in liner.
2. Description of the Related Art
Compared to vertical oil and gas wells, conventional horizontal well bore profiles focus on well bore sections that increase the surface area of the producing formation. Many of these producing formations do not readily release their contents until some form of well stimulation is conducted. Stimulation methods often use fluids to fracture the formation to provide additional exposed surface area. Such hydraulic operations have proven beneficial to increase production rates by fracturing the producing formation with fluids that contain proppants such as sand granules. Once in position, proppants maintain an open fracture in the formation that results from the fracturing process. Open fractures aid in allowing the petroleum products to exit the formation and be produced at the surface.
Initially, oil and gas wells were completed by perforating a string of production casing in selected locations. A stimulation process would then be conducted with all perforations exposed to the same fracturing operation. This method does not control the fracturing operation to ensure that each area of perforations receives the same amount of proppant.
An alternative completion method uses independent placement of perforations above a frac or bridge plug, followed by a fracturing operation of that set of perforations. Subsequently, another plug would then be set up hole to separate the perforations, and the operation would be repeated. This type of completion requires numerous trips in and out of the well with various assemblies. It also creates a significant amount of standby time for the surface equipment on location.
More recently, selective hydraulic fracturing of horizontal well bores has been accomplished with combinations of open hole packers and sliding sleeves that are installed at various intervals in the casing string. Each sliding sleeve is located between a pair of packers that control and force the fracture fluid into the formation.
This design, however, has its limitations as they require open holes in order to operate. As a result, these open hole packers have an inherent differential pressure limitation as they attempt to isolate adjacent formation sections. Due to the relatively short contact length that the packer element has with the formation, leak paths can occur during frac initiation. Once this leak path occurs the selective or independent frac feature is compromised. In addition, this open hole frac assembly is incompatible with a cement-in liner application. The material or cement in the annulus surrounding the frac ports blocks communication with the formation. Various methods have been attempted to penetrate, erode or dissolve the cement that blocks the frac access or limits the frac penetration of the surrounding formation. The complexity of these methods raises the cost of completion and increases the required time to complete the well. Thus, improvements in the design and implementation of stimulating wells would be desirable.